Exhaust help

[jjgrizz73]

Hey everyone, I currently have a N/A spyder and Im doing a 4g63t swap with these mods:
-MHI Evo III big 16g turbo
-Greddy 24V FMIC
-Greddy upper and lower intercooler piping
-Greddy Type RS BOV
-Apexi SAFC II
-Greddy Turbo Timer
-Slowboy Racing 3500 clutch
-Slowboy Racing ported 02 housing
-Walbro 255lph fuel pump
-Tubular turbo exhaust manifold
-TurboXS boost controller
-Cometic Head gasket
-ARP Head studs
-SS oil feed line
-Chrome smoked TB elbow
-Magnecor KV85 Competition spark plug wires


I have a brand new 2.5" exhaust cat back on it and obviously I need a new downpipe and high flow cat. Now can I get a 3" d/p and cat and use my exhaust still and if not would using 2.5" all the way restrict it that badly? I do plan on upgrading to a better exhaust (3") when I get some more cash but Im kind of low right now...

 

[architechnik]

The stock system is 2.25, so leaving it at 2.5 is still considered an upgrade from an entirely stock turbo system. You're using an internal waste gate and boost creep is rather common when you get into the 3" systems without porting the turbo exhaust housing; something to consider before making the purchase.

You'll do just fine with your setup for a DD and ensure consistent, even performance. If you're looking for really high top end, you may want to upgrade.

With the MHI EIII16g you'll likely not notice the restrictions until you hit about 300hp or revving above 6k. What are your primary hp goals and what size injectors are you dropping into this swap?

 

[jjgrizz73]

I'd like to just get to about 300 maybe slightly more and I'm thinking for right I'm going to use the evo's 550s for now and pick up some cams.

 

[architechnik]

If you're picking up cams, then you have a good deal higher flow capabilities. That can dramatically change where you want to be on the exhaust flow and you might want to look into getting a full 3". With that turbo, cams slightly higher than stock turbo (~268), and all those other supporting mods and a good tune you should easily hit about 300.

I would suggest larger injectors if you're going to go with more than 15lbs on the 16g. Do you have an EPROM or are you stuck with only the SAFC? You're limited to around 650cc's if you only have the piggyback but if you can get a chip, then some 750's would be ideal. Your IDC's will be rather high if you try to use the 550's with higher boost, running the risk of going lean.

EDIT: I didn't notice any Wideband O2 on your parts list. Do you have one for the tune or are you guessing?

 

[jjgrizz73]

Still have to pick that up along with the guages, I just wanted to kno mechanically sorry if some parts were alittle silly on there, I just copied it from cardomain

 

[jjgrizz73]

Ok so is the wideband o2 extremely ness. for right now? Or with a A/F guage and the S-AFC II will I be able to tune it fine?

 

[architechnik]

A narrowband O2 sensor is nearly worthless for tuning. It acts more like an On/Off switch that is tuned for fuel efficiency, a 14.7:1 ratio of air to fuel. The engine will only look at predefined maps that match rpms, manifold pressure, and fuel to a specific number when accelerating or use the input from the sensor to change the amount of fuel.

DO NOT buy an A/F gauge that you tap into the ECU lines. It will just oscillate back and forth and not make the least bit of sense for tuning. It really is just a ricer toy for filling up excessive pods.

The Wideband O2 controller and gauge will tell you if you're running rich or lean and provide a good readout. There are some basic tuning methods that just say keep it rich when boosting (between 10:1 and 12:1) and idling and cruising around 14.5:1. The A/F is the primary tool for tuning any vehicle and will be used most frequently.

A logger will help track other sensors to get a better tune, especially with knock:
Logging knock is almost equally important, especially when you get into high boosting. With compressed air, the engine becomes much hotter and, without alternative cooling methods, requires more fuel to act as a coolant.

If there is not enough fuel (or methanol/water injection) the small amounts of fuel that are supplied will detonate before the sparks fire, causing knock. The knock can cause damage as it fires the cylinder before it is in the correct stroke position, causing extreme stress on the engine.